One purpose of this project is to evaluate the cardiopulmonary effects of increasing intracranial pressure. We have found that the rate of change in intracranial pressure, not just the absolute magnitude of the intracranial pressure, is an important determinant of the cardiovascular response to increased intracranial pressure. Further, we have found that increasing intracranial pressure after moderate hemorrhage results in a markedly hyperdynamic cardiovascular response which led to a high output cardiovascular collapse in most animals. We plan to extend these observations and to systematically study the effect of altering respiratory parameters such as tidal volume, respiratory rate, inspired gas mixture, and positive end expiratory pressure on the cardiovascular responses to increased intracranial pressure.